1. Field of Invention
The present invention relates to a key assembly, and more particularly, a key assembly using sensors to sense the external state changes, so as to make the electronic device perform a preset function.
2. Related Art
The common electronic devices used in daily life or controlling equipments such as processing equipments used in industry all have key-in structure for controlling the above equipments. The conventional key structure substantially comprises spring-type structure and film-type structure. In the spring-type key structure, a pin is disposed on one side of the key body with respect to an electrical switch of the electronic device, and a spring is disposed between the key body and the electrical switch. When the user presses the spring-type key, the pin of the key body triggers the electrical switch by the elastic force of the spring, such that the electronic device performs the preset function corresponding to the electrical switch, and due to the elastic recovery characteristic of the spring, the key returns to its original position after being released. The film-type key structure is made of rubber, and the film-type key structure is disposed in the pre-designed key area of the electronic device. When the film-type key is pressed, the protrusion under the key structure is in electrically contact with the electrical switch corresponding to the key area, such that the electronic device performs the preset function corresponding to the electrical switch, and the film-type key returns to its original state due to the elastic characteristic of the rubber itself.
No matter the spring-type key structure using the spring for elastic recovery or the film-type key structure made of rubber, after being used for a long time, the elastic fatigue of the material occurs, thus influencing the sensitivity of the key structure, such that the key structure cannot certainty electrically contact with the electrical switch thoroughly. In order to accommodate the key body, spring, and electrical switch of the spring-type key structure in the conventional art, and due to the travel distance required when the spring-type structure is operated, the designed space of the electronic device is excessively large, thus the volume cannot be reduced, which cannot meet the requirements for the current electronic device of being light and thin.
In addition, in Utility Model NO. M246788 “Thermal Character and Symbol Inputting Apparatus and Key-in Unit thereof” issued in ROC Patent Gazette on Oct. 11, 2004, a plurality of thermal sensors is disposed on each key operating area on the surface of the keyboard substrate. When the user presses the key operating area, the corresponding thermal sensor senses a temperature variable signal, and after the signal has been processed, a key signal corresponding to the position of the thermal sensor is sent out.
The Utility Model NO. M246788 can significantly reduce the space and travel distance required by the spring-type key structure in the conventional art, however, the used thermal sensors requires an excessively long time for sensing the temperature, and the size of the contact area between the user and the operating area also influences the sensitivity of the thermal sensor. In addition, when the thermal sensor is used under different climates or in the environment having extremely large temperature difference such as tropical countries or frigid countries, the practical climate must be considered to adjust the thermal sensors. If the user carries along the electronic device having the thermal sensor to travel all over the world, different temperatures and climates possibly cause the accuracy reduction of the thermal sensor.
Also, in the thermal key-in unit disclosed in the Utility Model NO. M246788, the user touches the operating area such that the thermal sensor senses the temperature change of the operating area. However, there is no mechanism or means for limiting and protecting the thermal sensor being disposed in the operating area, the user may touch the operating area of the unnecessary key by mistake and an operation error occurs accordingly, thus causing trouble and inconvenience when the user uses the thermal key-in unit.
The spatial travel distance occupied by the spring-type key structure in the conventional art is excessively large, thus the volume of the electronic device cannot be reduced. The thermal sensor disclosed in the Utility Model NO. M246788 cannot solve the problem of the reduction of the sensing accuracy of the thermal sensor caused by a large temperature difference of the environment, and in addition, no means for protecting and limiting the thermal sensor is disposed in the operating area, thus an operation error easily occurs for the key-in unit.